The invention relates to the field of forming fibrous structures from fibrous materials. More particularly, the invention relates to a process for cohering a multitude of fibrous layers with a predetermined distribution of Z-fiber bundles that pass between adjacent fibrous layers.
Needling processes for forming fibrous preform structures for use in composite structures have been known for many years. U.S. Pat. No. 3,772,115 to Carlson et al. describes a process whereby several fibrous layers may be needled together simultaneously or in a series of needling steps. The Carlson et al. needling process involves repeatedly driving a multitude of barbed needles into the fibrous layers. The barbed needles displace fiber within the layers which causes the layers to adhere into a coherent structure. The structure may be incrementally formed by adding layers in a series of needling steps if the final structure is too thick to allow the needles to pass all the way through. The fibrous layers comprise carbon or graphite fabric, or precursors thereof. A fibrous preform structure formed according to the process may be further processed into a carbon/carbon composite structure by deposition of a carbon matrix within the fibrous preform structure that binds the fibers together. The Carlson et al. process may be used to form various composite structures, including carbon/carbon brake disks.
A similar process is disclosed in Great Britain Patent Specification 1,549,687, published Aug. 1, 1979. This also discloses a process for forming a carbon/carbon composite material. The fibrous layers may be comprised of oxidized polyacrylonitrile cloth which are needled together in a series of needling steps. In one example, the process was used to form a carbon brake disk.
A more recent process is disclosed by U.S. Pat. No. 4,790,052 to Pierre Olry. The goal is to produce a fibrous preform structure having a high degree of uniformity. This purportedly is accomplished by needling superposed layers together with a xe2x80x9cuniform densityxe2x80x9d of needling throughout the thickness of the article. The initial depth of penetration is determined as a function of the number of layers to be traversed by the needles, for example about twenty layers. The Olry et al. process attempts to keep this depth constant throughout formation of the fibrous preform structure by lowering the fibrous structure away from the needles a distance equal to the thickness of a needled layer each time a new layer is added.
U.S. Pat. No. 4,955,123, issued Sep. 11, 1990 and PCT Publication WO 92/04492, published Mar. 19, 1992, both to Lawton et al., describe a process whereby a brake disk is formed by needling together sectors of an annulus. The fibrous structure is lowered the thickness of a needled layer each time a new layer is added. U.S. Pat. No. 5,338,320, issued as a continuation in part from the ""123 patent on Feb. 14, 1995, to Smith et al. describes a process wherein outer layers of a preform are xe2x80x9cenrichedxe2x80x9d with staple fiber in a needling process. Enriching the outer layers in the Smith et al. process apparently increases mechanical strength in the outer layers and improves wear characteristics of a resulting disk brake.
In the fibrous preform art, the displaced fibers generated by the needling process are referred to as xe2x80x9cZ-fibersxe2x80x9d since they are generally perpendicular to the layers comprising a fibrous preform structure. The Z-fiber distribution throughout a brake disk can have a profound effect on disk wear life and on performance of the brake disk in slowing or stopping an aircraft. Therefore, a fibrous structure having a predetermined Z-fiber distribution and a method for forming a fibrous structure with a predetermined Z-fiber distribution are desired.
According to an aspect of the invention, a process is provided for forming a fibrous structure, comprising the steps of:
superposing and needling a multitude of fibrous layers together in a series of needling passes that generate a multitude of Z-fiber bundles within the multitude of fibrous layers, each needling pass generating a portion of the multitude of Z-fiber bundles that pass through adjacent fibrous layers, each portion of the multitude of Z-fiber bundles penetrating only those adjacent fibrous layers that need more Z-fiber bundles to attain a predetermined number of Z-fiber bundles within each fibrous layer in the multitude of fibrous layers.
According to another aspect of the invention, a process is provided for forming a fibrous structure, comprising the steps of:
cohering a multitude of fibrous layers in a series of needling passes, each needling pass comprising the steps of superposing at least one fibrous layer over fibrous layers previously cohered by previous needling passes, and generating Z-fiber bundles that extend from the at least one fibrous layer into the previously cohered fibrous layers, each of the previously cohered fibrous layers receiving Z-fiber bundles during subsequent needling passes until the number of Z-fiber bundles in that fibrous layer reach a predetermined number of Z-fiber bundles for that layer, each fibrous layer in the multitude of fibrous layers thereby having a predetermined number of Z-fiber bundles for that fibrous layer.
According to another aspect of the invention, a process is provided for forming a fibrous structure, comprising the steps of:
determining a desired number of adjacent fibrous layers to be penetrated by Z-fiber bundles for each needling pass such that the sum of Z-fiber bundles generated in each layer by each needling pass equals a predetermined number of Z-fiber bundles for that fibrous layer; and,
superposing and needling-the multitude of fibrous layers together in a series of needling passes that generate the multitude of Z-fiber bundles within the multitude of fibrous layers, the Z-fiber bundles generated by each needling pass penetrating the desired number of adjacent fibrous layers for that needling pass, thereby achieving the desired number of Z-fiber bundles for each fibrous layer in the multitude of fibrous layers.
According to another aspect of the invention, a process for making a fibrous structure is provided, comprising the steps of:
forming a multitude of Z-fiber bundles passing between fibrous layers within a multitude of superposed fibrous layers, the multitude of superposed fibrous layers including a first group having a lower fibrous layer and an upper fibrous layer, each fibrous layer within the first group having a portion of the multitude of Z-fiber bundles originating in that fibrous layer and passing through a number of fibrous layers disposed beneath that fibrous layer without passing through all of the fibrous layers disposed beneath that fibrous layer, the number of fibrous layers increasing from the lower fibrous layer to the upper fibrous layer.
According to another aspect of the invention, a fibrous structure is provided, comprising:
a multitude of superposed fibrous layers including a first group having a lower fibrous layer and an upper fibrous layer; and,
a multitude of Z-fiber bundles passing between fibrous layers within the multitude of fibrous layers, each fibrous layer within the first group having a portion of the multitude of Z-fiber bundles originating in that fibrous layer and penetrating subjacent fibrous layers without passing through all of the subjacent fibrous layers, the portions of Z-fiber bundles penetrating an increasing number of fibrous layers from the lower fibrous layer to the upper fibrous layer.
Thus, the invention provides a means for controlling Z-fiber distribution within a fibrous structure, and includes a fibrous structure having a desired Z-fiber distribution. The invention is particularly useful for making fibrous preform structures for carbon/carbon aircraft brake disks.